Since homeostasis in the T cell compartment plays a pivotal role in the etiology of autoimmune liver disease and immune-mediated liver injury, the focus in this section will be set on CEACAM1-mediated control in T cell activation and the induction of regulatory T cells and its implications in hepatic and mucosal immunity of the gastrointestinal tract. This evidence concerns the gene CEACAM1 and autoimmune hepatitis.